Wrist Instabilities & Dislocations

The wrist is a highly complicated and adaptable structure. Many small carpal joints enable significant motion in the coronal and sagittal planes and three-dimensional rotatory motions around the longitudinal axis with the radioulnar joints. The wrist is vulnerable to axial forces and deforming vectors due to its structure and the large range of motion. Despite this, the wrist remains surprisingly stable even with multidirectional external forces. The wrist maintains the balance between physiological forces and articulations due to intrinsic and extrinsic ligaments. The considerable high loads lead to an imbalance of equilibrium, and instabilities develop.

The extent of ligamentous or osseous lesions determines the degree of carpal instability. The word “dynamic” instability refers to a deformity that only happens while the wrist is in motion, while “static” instability occurs when the wrist is at rest. The main types of instabilities are Radiocarpal and mid-carpal instability. Treatment ranges from wrist braces to ligament reconstruction depending upon the extent of the injury.

Etiology

Acute Ligamentous Instability

Trauma
Indirect loading injury

Acute Bony Instability

Fractures

Chronic Instability

Repetitive microtrauma
Post-traumatic sequela (distal radius fracture)

Systemic Illness

Avascular necrosis of the scaphoid
Rheumatoid arthritis

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Neurological

Usually through the development of neurogenic arthropathies, i.e., Charcot-like joints
Syringomyelia.

Congenital Instability

Madelung deformity causes misalignment of the forearm (radius, ulna) and carpal bones, predisposing to progressive arthrosis and instability.

Epidemiology

A study by O'Brien revealed that there was a 44 percent cumulative rate of carpal instability during the second year after injury.
Malunion or growth arrest were the causes of secondary distal radio-ulnar joint (DRUJ) instability in 22% of cases in the J K Andersson study.
JB Tang observed an incidence of 30.6% after the distal radius fracture.
Scapholunate angles were found to be irregular in 39% of patients at presentation and 35% of patients after treatment in the distal radius fractures.
The incidence rates of distal radio-ulnar instability following the distal radius fractures are reported to be between 10% and 19%.

Pathophysiology

Mechanism

Carpal Instability Dissociative (CID)

Instability between bones inside a single carpal row is termed as CID. It may involve either the proximal or distal carpal rows, with the former being more common. It is classified into two types.

Scapholunate (SL):
- Most common CID instability pattern
- The scapholunate ligamentous complex and dorsal intercarpal ligaments stabilize this joint from distraction, torsion, and translation.
- Wrist extension, ulnar deviation, and carpal supination are the most common mechanisms of injury.
- Scapholunate dissociation leads to the scaphoid flexing palmarly and the lunate flexing dorsally.
- The main causes of SL instability are SL dissociation which may be an isolated or combined ligamentous injury or a displaced scaphoid fracture.
- Manifested radiologically as dorsal intercalated segment instability (DISI)
Luno-triquetral (LT):
- Lunotriquetral ligament, radio-lunate ligaments (both volarly and dorsally), and dorsal intercarpal ligaments play a key role in this joint stability.
- However, LT ligament disruption is the main reason for this instability.
- The radiological manifestation is as a Volar intercalated segment instability (VISI) pattern.
- Wrist hyperextension or extension, as well as radial deviation, may cause LT ligament injury.

Carpal Instability Nondissociative (CIND)

CIND does not have a specific distinction between proximal and distal carpal rows. Instead, it involves the whole carpal row, expressed at either the radiocarpal joint, the mid-carpal joint, or both. The pattern and anatomy are not well understood, with no specific classification or treatment.

It consists of two types:

CIND-VISI
- The three bones of the proximal carpal row rotate from flexion to extension when a typical wrist deviates from a radial-deviated to ulnar-deviated posture.
- This motion is maintained by extrinsic ligaments (triquetral-hamate-capitate ligament, dorsal radio-triquetral, and the anterolateral scaphotrapezial ligament) and intrinsic ligaments (ulno-lunate and lunotriquetral).
- Flexor carpi ulnaris and extensor carpi ulnaris play their role in moving the proximal row from flexion to extension.
- Palmar CIND develops when these underlying structures fail due to rupture, dispersion, and increased elasticity.
- The entire proximal row remains in flexion throughout the movement until the triquetral-hamate joint engages and the proximal row extends with a clunk.
CIND-DISI
- Attenuation of the Dorsal intercarpal ligament, long radio-lunate, radioscaphocapitate ligament, and Scapholunate ligament (Intrinsic) results in dorsal subluxation of the capitate.
- The dorsal subluxation occurs with the Ulnar deviation of the wrist.

Carpal Instability Complex (CIC)

There are combined patterns of injury between CID and CIND. There is damage or laxity to both volar and dorsal ligaments. The proximal row clunks into extension with ulnar deviation just like VISI-CIND. Furthermore, extremes of ulnar variance induce dorsal capitate subluxation, which is similar to dorsal CIND.

Adaptive Carpus Instability

The carpal ligaments are not usually broken or attenuated, but the dorsal tilt of the malunited distal radius and compensatory dinner fork extension of the proximal row reduce the distances between their origins and insertions. Therefore, Soft ligaments are unable to prevent capitate dorsal translation and distal carpal row.

Perilunate Dislocation

Peri-lunate dislocations are caused by damage to the surrounding balancing structures, such as fractures and articulation or ligament disturbances.

Intrinsic: scapholunate and lunotriquetral ligaments
Extrinsic ligaments (palmar): e.g., radio-lunotriquetral, radio-scapholunate, and ulna-lunate are the main stabilizing structures.

The lunate retains its articulated position with the distal radius while the surrounding carpal bones dislocate dorsally. Alternatively, the lunate can dislocate in the volar direction into what is known as the Poirier room, though this is uncommon.

Distal Radial-ulnar Joint (DRUJ) Instability

The volar/dorsal radioulnar ligaments and triangular fibrocartilage complex (TFCC) provide stability to the distal radioulnar joint. Painful pronation and supination following wrist trauma along with positive piano sign indicate distal radio-ulnar joint instability.

Treatment / Management

Treatment

Dorsal Intercalated Segment Instability (DISI)

Nonoperative

NSAIDs +- Immobilization is recommended for undisplaced ligamentous injury following a traumatic event.
Chronic asymptomatic injuries without arthrosis are usually treated conservatively.
Patient education, splinting, anti-inflammatory drugs, and brief courses of hand therapy should all be part of the treatment plan.

Soft Tissue Reconstruction

For refractory cases, surgical management may be attempted, but outcomes are not predictable.
Scapholunate ligament Repair: Scapholunate ligament repair is done on acute injuries without carpal malalignment. Recent studies have shown that the dorsal ligament is all that is necessary to maintain carpal alignment in the absence of radiographic evidence of the failure of the secondary stabilizers of the scaphoid.
Plication of Ligaments: Suturing the volar radioscaphocapitate ligament to the long radiolunate ligament and closing down the space of Poirier. sixteen out of eighteen patients showed decrease pain at rest and activity.
Bruneli & Brumeli procedure: Flexor carpi radialis is used to connect the lunate and scaphoid. Flexor carpi radialis tenodesis through the scaphoid and protected with dorsal wrist ligaments has shown encouraging results in a modified Brunelli technique.

Explore more:

DISI (Dorsal Intercalated Carpal Instability)

Wrist Instabilities & Dislocations